In recent years, image processing devices for processing an endoscopic image based on imaging by an image sensor have gained in popularity (e.g., see Patent Literature 1). Meanwhile, a phenomenon may occur in which the endoscopic image is partially darkened by light shielding caused by, for example, the hood of the lens for transmitting light to the image sensor. Hereinafter, such an area darkened by light shielding in the endoscopic image is also simply referred to as “black area”. Moreover, a phenomenon in which such a black area occurs in the endoscopic image is also called “vignetting”.